A.M. Bruce

Multiple Superdeformed Bands in

Abstract Three superdeformed bands have been observed in 194Hg. The dynamical moment of inertia J (2) of all three bands is observed to increase by 30–40% over the frequency range ħω = 0.1–0.4 MeV. This phenomena can be understood in terms of the gradual alignment of pairs of high-j intruder orbitals within the framework of the cranked Woods-Saxon and Nilsson models including pairing. The calculations together with the observed J (2) behaviour of the three bands indicate that pairing correlations in the superdeformed minimum are rather weak.

^194

Abstract The γ spectra of the neutron-deficient nuclei 49 Mn and 49 Cr have been observed using the reactions 12 C( 40 Ca, p2n) 49 Mn and 12 C( 40 Ca,2pn) 49 Cr at E (Ca)=160 MeV.Radiation from 49 Mn and 49 Cr was identified by detecting recoil ions in a 0° mass separator. Data from γ-γ, recoil-γ and recoil-γ-γ coincidence spectra and recoil-γ angular correlations allowed the level scheme of 49 25 Mn 24 to be deduced up to 6 MeV (19/2 − ).The levels of the mirror nucleus 49 24 Cr 25 were observed to over 10 MeV (27/2 − ). Relative Coulomb energies for the mirror states were found to have a smooth J dependence. The rotation-like level spacing at low spin is interrupted at J =19/2 − , and this is interpreted as an alignment effect.

Hg and Their Dynamical Moments of Inertia

New results for the Coulomb energy differences in the A=47 mirror nuclei 47Cr and 47V for yrast states up to spin 312ℏ are presented and shown to agree with earlier predictions made within a deformed, crancked shell model approach. The observed total difference in Coulomb displacement energies at low and high angular momenta is also explained within the spherical shell model. The first example of alignment in an N=Z nucleus, 48Cr, is reported.

High-spin states in the mirror nuclei 49Cr and 49Mn

Abstract The microscopic structure of the M1 mode in 164 Dy (in which the M1 strength is fragmented over several 1 + states) has been investigated using the 165 Ho(t, α) 164 Dy reaction. The 3 + −8 + members of a proposed K π =1 + rotational band with a band head energy of 2.557±0.015 MeV were observed to be strongly populated in l =5 proton transfer. These results are not consistent with a collective interpretation of this state.

Mirror nuclei at high spin in the f72 shell

Abstract A Doppler shift attenuation measurement has been carried out to determine the collectivity of the superdeformed band in 150 Gd. The data was found to be consistent with a constant inband quadrupole moment of 17 ± 3 e b. This corresponds to a quadrupole deformation of s 2 ≈0.58. In addition the measurement has resolved important questions regarding the de-excitation of the band, confirming the rapid de-excitation of the superdeformed band in 150 Gd with more than 80% of the band intensity being lost over one transition.

The microscopic structure of the M1 mode in 164Dy

Abstract The g -factor of the K = I =25 isomer in 182 Os has been measured by observing the angular precession of the decay γ-ray angular distribution in an external magnetic field as g =+0.425 (8). This result is compared with predictions based on experimental g -factors of single-particle Nilsson orbitals in this mass region.

The collectivity and the de-excitation of the yrast superdeformed band in 150Gd

The two-quasiproton structure of 164Dy has been investigated in a study of the 165Ho(t, α) 164Dy reaction. The experiment was performed using a 37.3 MeV triton beam delivered by the Daresbury tandem Van de Graaff accelerator. Magnetic analysis of ejectile ions was achieved using a QMG/2 magnetic spectrometer, and ion identification and detection employed a hybrid gas-filled, multielement, focal-plane detector. The two-quasiproton strengths accessed in this reaction are discussed with reference to the detailed spectroscopy of 164Dy. In particular, a rotational band built on a Kπ = 1+ state, previously interpreted as a collective structure, was observed and assigned as a two-quasiproton excitation which at zero deformation is based on the spherical (h112)2 shell-model state. The structure of the octupole-vibrational band and that of other states in the final nucleus have been elucidated.

The g-factor of the K=25 isomer in 182Os

Abstract Three superdeformed (SD) bands have been observed in 194Hg and four (or five?) SD bands in 193Hg using the 150Nd + 48Ca reaction. All bands except for two in 193Hg show a steady increase in dynamical moment of inertia J (2) with rotational frequency. The two exceptional bands form a classical pair of strongly interacting bands. It is suggested that the strong interaction between the bands is caused by a softness to octupole deformation. Evidence is found for the existence of dipole transitions connecting bands of opposite signature in 193Hg. The strengths of these transitions suggest that they are probably E1 supporting the importance of the role of octupole vibrations. These data suggest the wider importance of octupole softness in enhancing E1 transitions in the SD feeding and decay mechanisms. The spectroscopy of the observed SD bands in 193,4Hg are discussed in detail and attention is drawn to the “identical” energies of γ-rays in these isotopes with those in lighter isotopes. The similarities in bands relate to the neutron sub-shell closure for SD nuclei at N=112.

Two-quasiproton configurations in dysprosium-164

Abstract Questions on the validity of the K-selection rule for the decay of high spin isomers in deformed nuclei has been raised and an alternative mode by barrier penetration has been proposed. The present paper reports on a sensitive study of a K = 14 isomer in 174Hf where 20 different branches decay from the same level and consistently show low hindrance factors. It is found that the hindrance factors depend on K but have smaller absolute values than expected. The question of a barrier penetration decay mode is still open.

Evidence for octupole softness of the superdeformed shape from band interactions in 193,4Hg

Abstract The two-quasiproton structure of 174 Yb has been investigated in a study of the 175 Lu(t,α) 174 Yb reaction. The reaction was performed using a 35.5 MeV triton beam delivered by the Daresbury tandem Van de Graaff accelerator. Magnetic analysis of ejectile ions was achieved using a QMG 2 magnetic spectrometer and ion identification and detection employed a hybrid gas-filled, multielement, focal plane detector. Elements of the detailed nuclear structure of 174 Yb are discussed in terms of the two-quasiproton configurations populated. Of particular interest is a low-lying K π = 3 + band, observed in this reaction and discussed in terms of hexadecapole collectivity. No K π = 1 + bands were observed, and the consequences of this for a microscopic description of the magnetic-dipole-strength distribution in 174 Yb are discussed.